The present invention relates to a throttle control for improving the driveability of an automobile.
Virtually every driver of an automobile has observed that as the speed of the vehicle increases, the engine becomes less responsive to demands made upon it to further increase the vehicle speed. As a result, the average driver customarily causes the throttle to open an excessive amount when a speed increase is desired causing the vehicle speed to overshoot. The driver then eases off the throttle, again usually excessively, so that the vehicle speed undershoots the desired speed, again requiring the driver to increase the throttle opening. Experienced drivers are so accustomed to this phenomenon that they perform without conscious effort the necessary hunting action to achieve the proper throttle opening to produce the desired vehicle speed. If they were relieved of this burden, drivers would experience less fatigue on long trips and would gain the impression that the performance of their car was greatly improved and would be less inclined to buy and operate overpowered automobiles.
It has been determined through linear mathematical analysis of an engine-transmission-chassis automobile model that the transfer function between vehicle speed N (output) and throttle command O (input) can be represented by a LaPlace transform of the form: ##EQU1##
To one versed in control system synthesis, this transform typifies a second order lag network. In the case of an automobile, however, the coefficients T.sub.1 and T.sub.2 are not constants but are each variables. As will be shown T.sub.1 is substantially smaller than T.sub.2 and varies inversely as vehicle speed. T.sub.2, the larger coefficient, varies directly as vehicle speed and inversely as manifold pressure.
The concept of the present invention is based upon the recognition of the variable nature of the response of an automobile to changes in the speed command, the identification of the factors which create such variability of response, and the realization of means for modifying the speed command to the automobile engine in such a manner that the variability of response is practically eliminated. It is to be emphasized that the purpose of the invention is not to increase the performance of the vehicle in terms of maximum acceleration or modify exhaust emission controls, but to improve its driveability. That is, the invention will eliminate the vehicle's variable response and hence eliminate the necessity for the vehicle operator to hunt for the proper throttle setting to achieve the desired vehicle speed. The overall vehicle response then, becomes predictable.
More concisely, it is an object of the present invention to control with greater certainty, the throttle movement required to produce a desired vehicle speed.
A related object of the invention is to provide a vehicle speed control system which will relieve the operator of strain and annoyance during operation of the vehicle under varying conditions imposed by traffic or by the road.
Briefly, the invention comprises, in an automotive vehicle, means for sensing the vehicle speed, or related variable such as engine speed, means for sensing the engine manifold pressure and means for sensing the throttle angle commanded by the vehicle operator. A servo-mechanism is interposed in the linkage between the vehicle throttle control, which may be an accelerator pedal, and the throttle so that movement of the throttle is modified in a determinable manner. The modification to the throttle position commanded by the operator includes adjustment of the amplitude thereof by a factor comprising the quotient of the vehicle speed divided by the manifold pressure. More particularly, the throttle command, is adjusted in amplitude to include the effects of speed, manifold pressure and other engine parameters, then differentiated and added to the operator set throttle command for application to the engine throttle. By modifying the throttle command in this manner, the variable vehicle response to transient throttle command is replaced by a determinable response thus improving vehicle driveability. A further embodiment of the present invention illustrates its applicability to an engine equipped with a dual throttle.